1. Field of the Invention
The present invention relates to information bearing bar codes, and more particularly, to bar codes of the type which are arranged to be optically scanned by means of a hand-held light pen or wand. It is a primary object of the invention to provide a new and improved bar code arrangement wherein individual characters of the bar code are extremely small and may be detected by means of a decoding arrangement which is substantially independent of the manual scanning speed with which the light pen is moved over the label or ticket containing the bar code, while at the same time providing an arrangement wherein the code may be accurately scanned without repeated passes over the label and with a minimum of substitution and transposition errors.
2. Brief Description of the Prior Art
It is well known to use an optical scanner to capture data from a bar code. Typically, the optical scanner includes a source of illumination and a photodetector. The scanner is manually drawn across a bar code comprising a series of variable-width bars and spaces. During the scan, apparatus is provided to measure the time which it takes the optical scanner to pass over each bar and space within the code. The resulting series of time measurements correspond roughly to the width of the bar and space elements of the code and may be decoded to represent the data content of the code. Such a system is disclosed in U.S. Reissue Pat. No. Re. 28,198 which issued to the present inventor on Oct. 15, 1974.
Systems of the type just described have come into relatively widespread use. They are used, for example, to bar code price tags at the checkout counters of department stores and also to read inventory labels in automated industrial inventory-control systems. Customarily, the bar code is printed in association with a human readable set of characters so that the purchaser can himself identify the price, and other information associated with the article bearing the label.
While these systems are satisfactory for their intended purposes, the individual who handles the scanning stylus must be careful to draw the tip of the stylus directly over the printed bar code from one end of the code to the other. If the stylus slips off the edge of the bar code, then the data is not read correctly. Similarly, if dirt spots, gouges, or other irregularities are scanned, data is not normally collected and the scan must be repeated. Accordingly, it is sometimes necessary to scan the same bar code a number of times before the encoded data is properly read.
Also, with conventional bar code readers it is also necessary to have the length of the bars several times the height of the accompanying characters which are human readable so that the bar code occupies a relatively large space and requires a relatively large label.
Since the velocity with which the tip of the stylus moves over the printed bar code varies with different operators, the time taken to pass over each bar and space may vary over quite wide limits. In order to correct for such velocity changes, it is customary to store all of the digits of a particular character and from such storage determine through suitable logic the actual width of the bars and spaces. While various arrangements have been proposed for such velocity correction, all of them require additional logic and the storage of a large number of bits of information, all of which increases the complexity of the decoding apparatus. It would, therefore, be desirable to provide a scanning arrangement wherein the decoding of the bar code is independent of the velocity with which the manual scanner is drawn over the bar code.
Various other arrangements have also been heretofore proposed for scanning labels at constant velocity wherein a moving label is scanned by a rotating mirror, or the like. Such arrangements are shown, for example, in Stites et al U.S. Pat. No. 3,225,177 and Wolff U.S. Pat. No. 3,744,026, but are unsuitable for adaptation to hand-held scanning units due to the size, weight and complexity of such arrangements.
In addition to the above described bar code readers, it has also been proposed to provide only human readable characters on the label which are read directly by means of a hand held scanning unit. These arrangements have employed a photoelectric cell matrix on which is optically focused each OCR character as the scanner unit is moved across the label. Each character is compared with a series of masks corresponding to the characters to be recognized and when the scanned data corresponds to a particular mask, entry of the corresponding character is made. Such an OCR type of hand held scanning arrangement requires a relatively complex decoding arrangement for scanning the matrix in both horizontal and vertical directions and in order to provide a system which is not too expensive, the number of characters which can be recognized is limited to approximately twenty-one, so as to simplify the character recognition decoding process. The use of only twenty-one characters severely limits the clarity with which a message may be encoded by this method since a large proportion of characters are required for numbers, thus leaving only a few letters to convey the remaining desired information in human readable terms. Furthermore, the degree of skew which the hand scanner may assume with respect to the scanning path is severely limited in such OCR readers and a maximum skew limit of eight degrees may, in some instances, be required. Also, since the photoelectric cell senses the label over a substantial area and hence over a substantial width along the scanning path, the hand-held scanner unit must be maintained perpendicular to the plane of the label as the scanning operation is performed since otherwise portions of the light pattern striking the matrix will become defocused and reduce the reliability of detection of the character. As a result, the geometry and accuracy of printing which is to be read by such OCR hand scanners must be held to a very close tolerance. In addition, there is no way for the OCR reader to detect that an improper substitution has been made in the decoding process. Thus, if due to voids or smears in the printing operation a "2" becomes damaged so that it is read as a "3", there is no detection of this error and the wrong price may be decoded. Furthermore, since these voids and smears may be extremely small the operator who is using the hand scanner cannot visually detect the damage and hence is unaware of the substitution error.
Systems of the type just described have come into relatively widespread use. They are used, for example, to bar code price tags at the checkout counters of department stores and also to read inventory labels in automated industrial inventory-control systems. These systems are highly satisfactory. However, the individual who handles the scanning stylus must be careful to draw the tip of the stylus directly over the printed bar code from one end of the code to the other. If the stylus slips off the edge of the bar code, then the data is not read correctly. Similarly, if dirt spots, gouges, or other irregularities are scanned, data is not normally collected and the scan must be repeated. It is sometimes necessary to scan the same bar code a number of times before the encoded data is properly read.